feat(tui): lazygit-style titled panel borders

All panels wrapped in titled rounded borders (╭─ Title ──╮). Focused
panel gets accent-colored border, unfocused panels get muted border.

- Monitors panel: titled "Monitors", focused when detail is closed
- Logs panel: titled "Logs", always unfocused (passive display)
- Detail panel: titled with monitor name, focused when open

Table's own RoundedBorder replaced with HiddenBorder — the titled
panel border provides the visual frame, table uses space-separated
columns internally. Consistent chrome across all panels.

internal/tui/panel.go

@@ -0,0 +1,52 @@
+package tui
+
+import (
+	"strings"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+func (m Model) titledPanel(title, content string, width int, focused bool) string {
+	borderColor := m.theme.Border
+	titleColor := m.theme.Muted
+	if focused {
+		borderColor = m.theme.Accent
+		titleColor = m.theme.Accent
+	}
+
+	bc := lipgloss.NewStyle().Foreground(borderColor)
+	tc := lipgloss.NewStyle().Foreground(titleColor).Bold(true)
+
+	innerW := width - 2
+	if innerW < 10 {
+		innerW = 10
+	}
+
+	titleRendered := tc.Render(" " + title + " ")
+	titleLen := len([]rune(title)) + 2
+	fillLen := innerW - titleLen - 1
+	if fillLen < 0 {
+		fillLen = 0
+	}
+
+	top := bc.Render("╭─") + titleRendered + bc.Render(strings.Repeat("─", fillLen)+"╮")
+
+	contentStyle := lipgloss.NewStyle().Width(innerW).MaxWidth(innerW)
+	inner := contentStyle.Render(content)
+
+	var lines []string
+	lines = append(lines, top)
+	for _, line := range strings.Split(inner, "\n") {
+		lines = append(lines, bc.Render("│")+line+strings.Repeat(" ", max(0, innerW-lipgloss.Width(line)))+bc.Render("│"))
+	}
+	lines = append(lines, bc.Render("╰"+strings.Repeat("─", innerW)+"╯"))
+
+	return strings.Join(lines, "\n")
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}